Help me understand what’s going on electrically in my house. I understand the basics of an electric circuit, but my knowledge is limited.
In my kitchen, one of the lights is on a dimmer. I noticed recently that if I turn on the microwave while the light is dimmed, it gets brighter while the microwave is running.
I could understand it getting dimmer when the microwave ran. Microwaves use a lot of energy, so maybe there’s enough voltage drop to make the lights dim. But what’s going on that turning on another appliance (that’s presumably on the same circuit) results in more current going to the light?
My best guess is that whatever the dimmer uses to dim the light has a very non-linear response to something else in the system.
I don’t have an answer, but it we might need to know if it’s an old rheostat type dimmer or a newer triac type one. Also, incandescent, LED or CFL bulbs?
The only thing I can think of is that the microwave, sucking up some of the available power is messing with the dimmer…
…however, doing some reading, I am seeing that lights getting brighter when something with a high demand for power turns on is a symptom of a loose neutral somewhere in the system. I’ve done my share of shade tree electrical work, but that’s not something I’ve encountered and having just learned about it and only having read about it for a few minutes now, I’m not quite ready to guess at where it would be in your house.
But that leaves me with two more questions:
How comfortable are you poking around in your electrical boxes?
Do you have a voltage tester or multimeter?
Some devices use a voltage to control current flow. A lower voltage, allows more current to flow. Maybe your dimmer switch works like that. The microwave may cause enough of a voltage drop to alter the voltage in the control device. They are a particular type of transistor. A positive or negative voltage creates a field that limits current flow. But altering the supplied voltage before the device can change the flow that it was set at.
It might be more pronounced if your lights and microwave are on the same circuit. Same breaker. A microwave should be on a separate breaker.
It’s easy enough to test for, if you have a multimeter and know how to use it.
Most homes in the U.S. are fed from a split phase transformer (aka a center tapped transformer). You have 240 volts from one line to the other, and 120 volts from either line to neutral. You can think of the neutral as being the halfway point between the two line voltages.
If you’ve got a bad neutral, then as one line or the other draws more current, your voltages will go a bit out of whack. Instead of being 120 volts from either line to neutral, one may go up to 130 and the other may go down to 110. The outlets in your home should be roughly evenly distributed between the two lines, so you can measure the voltages at different outlets and you should be able to see if half of them go up and the other half go down when you run the microwave or any other high power device.
The bad neutral connection is most likely at the breaker box or at the utility pole, or somewhere in between.
WARNING!!!
A bad electrical connection is the sort of thing that can burn your house down. If you don’t know how to measure the voltages yourself, call the power company or an electrician and have someone check your home’s wiring.
Seriously, this isn’t something to shrug off. Worst case, you’re talking about something that can burn down your house and kill everyone inside. Get it looked at ASAP.
Thank you for all the information and for the clear warning. I’m definitely treating this as an urgent problem. The question is whether I try to look at it first or just call an electrician immediately.
It’s easy to determine if a bad neutral is a possibly.
Find out if the Microwave and dimmer are on the same leg. If they are, it’s not a bad neutral.
If they are on different legs, it’s a definite possibility.,
You can try snugging down all of the screws in your breaker box, in particular all of the ones on the neutral bus.
Ideally, you’d disconnect the power first, but if you know what you’re doing, it’s possible but foolish to do this “hot”
With any luck, your lights will stay the same brightness when the microwave is running after this. If not, you may have a loose neutral in the service entrance, which would usually be a job for your power company to address. Call them, tell them you think you have a loose neutral, and you’ll probably have someone show up inside of an hour. Loose neutrals really can be catastrophic, so if they can fix one before there’s a fire or equipment gets damaged, they’ll be right on it.
If no luck, you probably have a dodgy connection in the house wiring. Probably at some wire nut in a junction box, so the fun part is finding it.
As I said earlier, this is a new concept for me so I’m still learning about it. But ISTM a shared neutral could do it as well. A shared neutral, running to a kitchen with one hot going to an outlet and the other other going to lights, would be common.
That would be something to look for, even before tightening things. Same goes for if the OP wants to open up a few j-boxes in the kitchen (or that feed the kitchen) and see if any of them appear to go to both the outlet AND the lights. A few minutes of poking around with a DMM will show if they’re on the same branch (120 hot to hot) or different branches (240 hot to hot).
One of the reasons shared neutrals, while legal when done properly, should be avoided is that if the neutral becomes disconnected (in the breaker box), everything on the circuit is suddenly at 240 AND shutting off one breaker (With a broken neutral) won’t kill the circuit since it still has a path back to the box.
I believe the first problem I mentioned with a shared neutral is a similar concept for why a loose neutral can cause a high draw load to cause lights to get brighter on other circuits (specifically on the other leg). I’m of the understanding that the extra amperage that’s being pulled, instead of being sent back through the neutral, is (at least somewhat) sent back through the hot wire. If this is the case for the OP, it’s traveling through the light bulbs on the way there.
As for why it only happens when they’re dimmed, my guess would be that he’s not noticing it when they’re at 100%, or they just can’t get any dimmer.
You could, if you wanted to, check the voltage (with the dimmer at 100%) the voltage at the socket when the microwave is running, but I think that’s moot.
As mentioned previously, it sounds like a loose neutral connection. I had a similar issue with voltage fluctuations and called the utility company. They found a loose neutral at the meter, tightened it and all was well. A loose neutral can arc resulting in a fire.
That is a symptom of a loose neutral, as others have said. Given the possibility for fire from a loose neutral, electric utilities take those very seriously. If you call your local electric company, they’ll likely send someone out pretty quickly to check it out.
In the UK we apparently use a three-phase system in our homes. Does this mean that the above loose-neutral problem could not happen here? We live in a house with old wiring and I’d just like to know as this seems such a dangerous potential fault.
I don’t know where you get that idea. UK domestic supply is all 240V and single phase.
You should probably budget to have your house rewired as soon as finances allow. This will resolve any problems that exist from decaying insulation and amateur extensions and bring it up to the current code. You can also have loads of outlets added. Unlike American house wiring, your house has a number of circuits that start and finish at the distribution board, where the mains supply comes in. Some will be for power and some for light; possibly one for an electric cooker. You can happily plug a light into a power outlet, but should never connect anything over 100 watts to a lighting circuit.
There are three wires: a green or green and yellow one (maybe just bare wire) which is the earth, and two others, one of which is red or brown. This is the one that should always be wired to the switch.
I assumed that also covered British homes, especially as the following paragraph concerning the UK specifically did not mention any difference, but I may well have misunderstood.
Note that because the current is alternating, the 'live/neutral description above is purely convention so that switching is always on the ‘live’ (ie the same) side.
[QUOTE=aldiboronti]
I assumed that also covered British homes, especially as the following paragraph concerning the UK specifically did not mention any difference, but I may well have misunderstood.
[/QUOTE]
Overall distribution is 3 phase, individually each phase is 230V - you only get one phase delivered to your house.
Wow. I never thought about the circuit being loose at the pole. Of course, the good news is that it’s not inside wiring, so no electrician cost or somewhat-risky DIY to tighten the neutral in the breaker box (which is where the conversation up to now seemed to be going).
(Although E_C_G did point out that the issue could be at the pole. Good call, that.)
Crossing fingers that this was the root cause and that all is good.
Um, I wonder if I could take this on a little hijack since I have a kinda similar problem in my house?
I am getting ready to do some electrical work to my house, but mind that I haven’t done it yet. So this problem can’t be something I have done!
Noticed this morning an issue with lights pulsating. Kids and wife advised this has happened before recently, I just hadn’t noticed it.
The lights just barely dim, I’d estimate 3-4 times/second for 4-5 seconds. Then they were steady for 20-30 seconds and do it again.
My first thought was that the CFL bulb in the fixture was starting to go out and I planned on replacing it tonight. Then I went in to the adjacent room, a light there was doing the same thing.
No motors running…coffee pot was on, now that I think about it. Could have been the heating element kicking on? Not sure if it’s on the same circuit or not, as I’ve only begun tracing everything. Wouldn’t be surprised, though. A neutral problem would effect the rest of the house regardless, correct?
Guess I can check that when I get home, but in the meantime any other ideas? Thinking about this thread and poking around I thought it had some of the same symptoms.